How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Started Apr 19, 2010 | Discussions
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Robsphoto
Robsphoto Senior Member • Posts: 1,218
How do you calculate the reach advantage? Sony A900 vs Nikon D3S

I have written some notes about the advantages and disadvantages of cropping images to gain extra reach, that you can see here:

http://www.robsphotography.co.nz/focal-length.html

The other day, I was talking to some friends about the differences between the full frame 24.6 megapixel Sony A900, and the full frame 12.1 megapixel Nikon D3S.

It’s clear, of course that, when you are comparing two full frame cameras, if you put a 300mm lens on both, the reach of the A900 and the D3S is the same, that is, 300mm.

Or is it? Does this take into account that the pixel density of the A900 (in pixels per linear centimetre) is about 42% greater than that of the D3S (1685 vs 1182)?

So, after a while, we decided that, provided the images from both the A900 and the D3S were not cropped and kept the same 300mm field of view, the reach of both cameras is the same.

But, when both images have the SAME FIELD OF VIEW , because of the higher pixel density of the A900, the image width of an A900 image (6048 pixels) is about 42% greater than the comparable image width of an image from the D3S (4256 pixels).

But, what if an image from the A900 is cropped from its original width of 6048 pixels to the SAME IMAGE WIDTH as an image from the D3S, that is, 4256 pixels?

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

So, how do you define the term “reach”? Do you agree with the conclusions we came to?

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

Thanks very much for your feedback.

Regards
Rob
http://www.robsphotography.co.nz/SonyA900-NikonD3S.html

Analysis of the pixel density advantage of the Sony A900 compared with the Nikon D3S

Dennis Forum Pro • Posts: 17,105
Reach is the same

Robsphoto wrote:

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

No. Admittedly, there's an element in the crop factor argument that says that using an APS-C sensor "beats" cropping FF because state of the art APS-C is more dense than state of the art FF, so you generally have more MP in the APS-C image than the cropped FF image .. and if you follow that line of thinking, the same applies to A900 versus D3S.

But ultimately, that's all it is: an advantage. Not more reach.

You can crop either equally, and you simply end up with more MP in the A900 file than the D3S file, just as if you didn't crop at all.

Saying the A900 has more reach would be kind of like saying Ektar has more reach than Gold Max.

The other thing to consider is that just because you have more photosites on the sensor doesn't mean you're necessarily capturing more detail. You need good lenses & good technique. You can always uprez the D3S file and have an even bigger file than the A900 gives you ! It shouldn't have more detail.

The point being, all the A900 gives you is the potential for recording more detail. Cropped, not cropped, only potential. There's always been an argument in favor of higher res sensors (whether FF or APS-C) saying that the higher res sensor gives you more room to crop. That's what it boils down to. Assuming you're capturing the detail in the first place, you have more room to crop. "More reach" is a different way of looking at the issue, but since everyone understands "more room to crop" and everyone understands "reach" I think it's simpler to leave the definitions alone.

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

Same FOV.

Honestly, I didn't look at the math, but I assume it's based on pixel counts. I'd want to see sample images. If you compare the resolution of the D3S and A900 as tested here by dpreview, you see that the extinction resolution shows the 1.4X difference you'd expect, but the tested 'absolute' resolution gives the A900 only a 22% increase over the D3S. Whether you agree with these or not, the basic thought here is that the captured detail isn't necessarily dependent on the sensor resolution.

  • Dennis

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Cyrus84 Senior Member • Posts: 1,862
Re: Reach is the same

Dennis wrote:

Robsphoto wrote:

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

No. Admittedly, there's an element in the crop factor argument that says that using an APS-C sensor "beats" cropping FF because state of the art APS-C is more dense than state of the art FF, so you generally have more MP in the APS-C image than the cropped FF image .. and if you follow that line of thinking, the same applies to A900 versus D3S.

But ultimately, that's all it is: an advantage. Not more reach.

You can crop either equally, and you simply end up with more MP in the A900 file than the D3S file, just as if you didn't crop at all.

Saying the A900 has more reach would be kind of like saying Ektar has more reach than Gold Max.

The other thing to consider is that just because you have more photosites on the sensor doesn't mean you're necessarily capturing more detail. You need good lenses & good technique. You can always uprez the D3S file and have an even bigger file than the A900 gives you ! It shouldn't have more detail.

The point being, all the A900 gives you is the potential for recording more detail. Cropped, not cropped, only potential. There's always been an argument in favor of higher res sensors (whether FF or APS-C) saying that the higher res sensor gives you more room to crop. That's what it boils down to. Assuming you're capturing the detail in the first place, you have more room to crop. "More reach" is a different way of looking at the issue, but since everyone understands "more room to crop" and everyone understands "reach" I think it's simpler to leave the definitions alone.

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

Same FOV.

Honestly, I didn't look at the math, but I assume it's based on pixel counts. I'd want to see sample images. If you compare the resolution of the D3S and A900 as tested here by dpreview, you see that the extinction resolution shows the 1.4X difference you'd expect, but the tested 'absolute' resolution gives the A900 only a 22% increase over the D3S. Whether you agree with these or not, the basic thought here is that the captured detail isn't necessarily dependent on the sensor resolution.

  • Dennis

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While I agree with you on most of these points, I think it is good to get the word out SOMEHOW to beginners that the A700 doesn't get more reach than the A900, it just has slightly more pixel density for what part of the sensor it covers.

Kind of an aside I guess, but it bothers me when people continually say you should buy the A700 over the A850/A900 purely because of the "Extra reach." If you want lower price or higher FPS or something that the A700 offers, thats fine... but extra reach is just an illusion.
--
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Klipsen Veteran Member • Posts: 6,150
Lens resolution must meet or exceed sensor resolution

In addition, the picture must be precisely focused.

Only then can you crop with a decent result, and only then will you have a crop advantage.

Maybe it should be called an "enlargement advantage", because you can easily crop a 12 Mpix full frame image to APS-C size and still get a more than decent A4 print (circa 8"x12").

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Robsphoto
Robsphoto OP Senior Member • Posts: 1,218
Reach advantage = pixel density advantage?

Dennis wrote:

Robsphoto wrote:

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

No. Admittedly, there's an element in the crop factor argument that says that using an APS-C sensor "beats" cropping FF because state of the art APS-C is more dense than state of the art FF, so you generally have more MP in the APS-C image than the cropped FF image .. and if you follow that line of thinking, the same applies to A900 versus D3S.

But ultimately, that's all it is: an advantage. Not more reach.

You can crop either equally, and you simply end up with more MP in the A900 file than the D3S file, just as if you didn't crop at all.

Saying the A900 has more reach would be kind of like saying Ektar has more reach than Gold Max.

The other thing to consider is that just because you have more photosites on the sensor doesn't mean you're necessarily capturing more detail. You need good lenses & good technique. You can always uprez the D3S file and have an even bigger file than the A900 gives you ! It shouldn't have more detail.

The point being, all the A900 gives you is the potential for recording more detail. Cropped, not cropped, only potential. There's always been an argument in favor of higher res sensors (whether FF or APS-C) saying that the higher res sensor gives you more room to crop. That's what it boils down to. Assuming you're capturing the detail in the first place, you have more room to crop. "More reach" is a different way of looking at the issue, but since everyone understands "more room to crop" and everyone understands "reach" I think it's simpler to leave the definitions alone.

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

Same FOV.

Honestly, I didn't look at the math, but I assume it's based on pixel counts. I'd want to see sample images. If you compare the resolution of the D3S and A900 as tested here by dpreview, you see that the extinction resolution shows the 1.4X difference you'd expect, but the tested 'absolute' resolution gives the A900 only a 22% increase over the D3S. Whether you agree with these or not, the basic thought here is that the captured detail isn't necessarily dependent on the sensor resolution.

  • Dennis

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Thanks very much Dennis for your thoughtful reply. At a first glance, you would think that, when a 300mm lens is on two full frame cameras, there can be only one answer, that is, the reach of the two cameras is the same! And it certainly is the same if the pixel density of the two cameras is the same.

But, after participating in a Canon thread that touched on the topic of “reach”, one poster said that, clearly, “pixels per duck is the only thing that makes sense”.

http://forums.dpreview.com/forums/read.asp?forum=1032&message=35045202

And, when you compare the Sony A900 with the Nikon D3S, because of its 42% higher pixel density, the A900 would have more “pixels per duck”, and therefore has a 42% reach advantage.

In other words, some people consider that, the “reach advantage” is always equal to the “pixel density advantage” that one camera enjoys over another.

But I guess it all boils down to how you define the term “reach”, so that’s why I’m interested in the views of others on this point.

My main contribution to the Canon thread referred to above can be seen here:

http://forums.dpreview.com/forums/read.asp?forum=1032&message=35062506

In this posting, I attempted to show the relationship between reach and pixel density.

Regards
Rob
http://www.robsphotography.co.nz/focal-length.html
Advantages and disadvantages of cropping images to gain extra reach

DUSTY LENS
DUSTY LENS Veteran Member • Posts: 4,308
Re: How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Robs Photo ,

To calculate based on equal pixel count with each camera , you need to use one of the pixel dimensions either the width or the length from each camera sensor , and compare the same dimension length or width of each camera . Then using that , find the physical dimensions in each Camera which contain the same pixels per Length or width .

When you have these two dimensions you can just divide one by the other to find the factor of telephoto power for one camera compared with the other .

It is meaningless to compare without comparing equal pixel image resolutions .

Dusty

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Robsphoto
Robsphoto OP Senior Member • Posts: 1,218
Re: How do you calculate the reach advantage? Sony A900 vs Nikon D3S

DUSTY LENS wrote:

Robs Photo ,

To calculate based on equal pixel count with each camera , you need to use one of the pixel dimensions either the width or the length from each camera sensor , and compare the same dimension length or width of each camera . Then using that , find the physical dimensions in each Camera which contain the same pixels per Length or width .

When you have these two dimensions you can just divide one by the other to find the factor of telephoto power for one camera compared with the other .

It is meaningless to compare without comparing equal pixel image resolutions .

Dusty

Thanks Dusty, so to get "equal pixel image resolution" with the example I have given, you could crop an A900 image (6048 pixels x 4032 pixels) to the same image size as an image from the Nikon D3S (4256 pixels x 2832 pixels).

In these circumstances, would you agree that the "reach advantage" in favour of the A900 is about 42%, which is also equal to the 42% pixel density advantage (in linear terms)? This 42% reach calculation was explained in my opening post.

Regards
Rob
http://www.robsphotography.co.nz/focal-length.html
Advantages and disadvantages of cropping images to gain extra reach

Robsphoto
Robsphoto OP Senior Member • Posts: 1,218
A900 vs A700: reach advantage of A700 is 7.9%?

Cyrus84 wrote:

Kind of an aside I guess, but it bothers me when people continually say you should buy the A700 over the A850/A900 purely because of the "Extra reach." If you want lower price or higher FPS or something that the A700 offers, thats fine... but extra reach is just an illusion.

I agree that the "extra reach" of the A700 over the A900 is not very significant, in fact it is only 7.9%, as shown on this web page:

http://www.robsphotography.co.nz/crop-factor-advantage-s700-s900.html

Tell us whether or not you agree with the following calculations:

The 7.9% gain in reach (in favour of the A700) arises only because the pixel density of the A700 (in pixels per linear centimetre) is 7.9% greater than that of the A900 (1818 / 1685).

Calculation of reach advantage: Reach of A700 with a 300mm lens = 458.3mm (300mm x 35.9/23.5).

Reach of A900 when an image is cropped to the same image width as A700 = 424.7mm (6048 / 4272 x 300mm).

Gain in reach of the A700 = 7.9% (458.3mm / 424.7mm)

Regards
Rob
http://www.robsphotography.co.nz/focal-length.html
Advantages and disadvantages of cropping images to gain extra reach

Mike CH Veteran Member • Posts: 6,972
Capture time reach vs. output time reach?

It seems to me that reach is really FOV at capture time (leaving out such details as lens resolution etc).

Aren't you really saying that the reach at output time is better? Ie. you can produce - in PP - an image with comparable quality, but smaller FOV.

Regards,
Mike
--
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I know it has uses, but not for me.

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Robsphoto
Robsphoto OP Senior Member • Posts: 1,218
Re: Capture time reach vs. output time reach?

Mike CH wrote:

It seems to me that reach is really FOV at capture time (leaving out such details as lens resolution etc).

Aren't you really saying that the reach at output time is better? Ie. you can produce - in PP - an image with comparable quality, but smaller FOV.

You can increase the reach of an image by cropping, but this has its advantages and disadvantages as explained here:

http://www.robsphotography.co.nz/focal-length.html

In the example I have given at the start of this thread, the field of view (FOV) at capture time of both full frame cameras is 300mm, because a 300mm lens was used on both cameras. So, you could say that the reach of both cameras with a 300mm lens of the same quality is the same.

But, this ignores the fact that the pixel density of the A900 is about 42% greater than that of the Nikon D3S, and several people consider that, because of this, the reach of the A900 is also 42% greater than that of the D3S.

Regards
Rob

Mike CH Veteran Member • Posts: 6,972
Re: Capture time reach vs. output time reach?

Robsphoto wrote:

Mike CH wrote:

It seems to me that reach is really FOV at capture time (leaving out such details as lens resolution etc).

Aren't you really saying that the reach at output time is better? Ie. you can produce - in PP - an image with comparable quality, but smaller FOV.

You can increase the reach of an image by cropping, but this has its advantages and disadvantages as explained here:

http://www.robsphotography.co.nz/focal-length.html

In the example I have given at the start of this thread, the field of view (FOV) at capture time of both full frame cameras is 300mm, because a 300mm lens was used on both cameras. So, you could say that the reach of both cameras with a 300mm lens of the same quality is the same.

But, this ignores the fact that the pixel density of the A900 is about 42% greater than that of the Nikon D3S, and several people consider that, because of this, the reach of the A900 is also 42% greater than that of the D3S.

I see what you are getting at, but redefining reach to mean that is at best confusing. I think cropping advantage is a better word.

And I would watch out for the precision of those 42%. You have an assumption in the calculation, I think, that photosite/pixel is comparable across different sensor technologies.

Regards,
Mike
--
I'd prefer my DSLR without video, thank you.
I know it has uses, but not for me.

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Robsphoto
Robsphoto OP Senior Member • Posts: 1,218
Cropping power of the Sony A900

Mike CH wrote:

Robsphoto wrote:

Mike CH wrote:

It seems to me that reach is really FOV at capture time (leaving out such details as lens resolution etc).

Aren't you really saying that the reach at output time is better? Ie. you can produce - in PP - an image with comparable quality, but smaller FOV.

You can increase the reach of an image by cropping, but this has its advantages and disadvantages as explained here:

http://www.robsphotography.co.nz/focal-length.html

In the example I have given at the start of this thread, the field of view (FOV) at capture time of both full frame cameras is 300mm, because a 300mm lens was used on both cameras. So, you could say that the reach of both cameras with a 300mm lens of the same quality is the same.

But, this ignores the fact that the pixel density of the A900 is about 42% greater than that of the Nikon D3S, and several people consider that, because of this, the reach of the A900 is also 42% greater than that of the D3S.

I see what you are getting at, but redefining reach to mean that is at best confusing. I think cropping advantage is a better word.

And I would watch out for the precision of those 42%. You have an assumption in the calculation, I think, that photosite/pixel is comparable across different sensor technologies.

Thanks Mike, yes I guess you could use the term "cropping advantage", because in the example given, the "cropping power" of the Sony A900 is far greater than that of the Nikon D3S. But, when you crop an image from the A900 to the same image width as the D3S, you have increased the reach of the A900 image, and probably also the amount of visible detail is greater in the A900 image.

Even when the fields of view of two images are the same, if the image size produced by one of the cameras is considerably greater than the other, the larger image can disclose a lot more detail, and I guess some people might regard this as extra reach due to the increased pixel density.

Regards
Rob
http://www.robsphotography.co.nz

Mike CH Veteran Member • Posts: 6,972
Re: Cropping power of the Sony A900

Robsphoto wrote:

Mike CH wrote:

Robsphoto wrote:

Mike CH wrote:

It seems to me that reach is really FOV at capture time (leaving out such details as lens resolution etc).

Aren't you really saying that the reach at output time is better? Ie. you can produce - in PP - an image with comparable quality, but smaller FOV.

You can increase the reach of an image by cropping, but this has its advantages and disadvantages as explained here:

http://www.robsphotography.co.nz/focal-length.html

In the example I have given at the start of this thread, the field of view (FOV) at capture time of both full frame cameras is 300mm, because a 300mm lens was used on both cameras. So, you could say that the reach of both cameras with a 300mm lens of the same quality is the same.

But, this ignores the fact that the pixel density of the A900 is about 42% greater than that of the Nikon D3S, and several people consider that, because of this, the reach of the A900 is also 42% greater than that of the D3S.

I see what you are getting at, but redefining reach to mean that is at best confusing. I think cropping advantage is a better word.

And I would watch out for the precision of those 42%. You have an assumption in the calculation, I think, that photosite/pixel is comparable across different sensor technologies.

Thanks Mike, yes I guess you could use the term "cropping advantage", because in the example given, the "cropping power" of the Sony A900 is far greater than that of the Nikon D3S. But, when you crop an image from the A900 to the same image width as the D3S, you have increased the reach of the A900 image, and probably also the amount of visible detail is greater in the A900 image.

Yes, you have increased the reach of the final image, but not the reach of the sensor/lens combination in what I think is the traditional sense of the word.

But even defining reach as the FOV gets a bit complicated - because when you crop you also decrease FOV, and then you have increased reach. So I can see where you come from with the term - I just find it confusing.

Even when the fields of view of two images are the same, if the image size produced by one of the cameras is considerably greater than the other, the larger image can disclose a lot more detail, and I guess some people might regard this as extra reach due to the increased pixel density.

In the sense that you can produce an image after exposure which could also have been taken with a longer lens and less dense sensor, yes. Baring problems with lens/sensor resolution, of course.

But isn't that quite obvoius, really? I was for me, at least.

Regards,
Mike

PS: I spent 2 months on bicycle in NZ some 12-13 years ago - Auckland to Invercargill and back. Beautiful place.
--
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I know it has uses, but not for me.

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Cyrus84 Senior Member • Posts: 1,862
Re: Cropping power of the Sony A900

I'm thinking it is a lexicon issue, as everything you are saying makes sense in terms of getting a blown up picture of something small in the distance.

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

Cropping power could be the word, but I keep thinking magnification-- you are basically magnifying the center part of the picture and making it take up more of the frame. I just wouldn't want it to be confused with macro work.

I get what you're getting at and don't have an answer myself... I still think it is a good thing to be looking at because people assume that the APS-C sensors have 1.5 times more "reach" when they really are just 1.5 times more cropping power compared to the original FF image. Once you crop to the same size, it only has that 8% advantage you mentioned.
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Mike CH Veteran Member • Posts: 6,972
Re: Cropping power of the Sony A900

Cyrus84 wrote:

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

Are you sure about that?

If you change from 400mm to 300mm and also change you position to maintain the same the scene, then perspective changes.

But if you stay in the same place (rather, the optical center of the lenses stay in the same place), do the lens change and then crop to get the same scene, then perspective should stay the same.

No?

Regards,
Mike
--
I'd prefer my DSLR without video, thank you.
I know it has uses, but not for me.

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Dave Oddie Veteran Member • Posts: 4,073
No need to over complicate matters

Robsphoto wrote:

But, when both images have the SAME FIELD OF VIEW , because of the higher pixel density of the A900, the image width of an A900 image (6048 pixels) is about 42% greater than the comparable image width of an image from the D3S (4256 pixels).

But, what if an image from the A900 is cropped from its original width of 6048 pixels to the SAME IMAGE WIDTH as an image from the D3S, that is, 4256 pixels?

If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm)?

No, because when you crop the A900 image you end up with a different image than that of the D3S that hasn't been cropped.

So, how do you define the term “reach”? Do you agree with the conclusions we came to?

No.

When comparing the reach of two cameras, do you prefer the “same field of view” approach, or do you prefer the “same image width” approach?

It can only be the same field of view otherwise you end up with different images.

If you wanted to argue you can crop an A900 image more than that of a D3S image no one will disagree. That has always been true of higher mega-pixel cameras as the pixel count has increased but IMO people tend to crop to aid composition not to obtain reach.

I also agree with this comment from Dennis:

Saying the A900 has more reach would be kind of like saying Ektar has more reach than Gold Max.

That hits the nail on the head. Finer grained films were never thought to give a camera more reach compared to when they were used with a coarse grained film. You could just crop more before the grain became too obtrusive when using fine grained film.

No need to over complicate matters and move away from well understood concepts IMO.

Dave

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copejorg1 Senior Member • Posts: 1,626
Re: A900 vs A700: reach advantage of A700 is 7.9%?

Robsphoto wrote:

I agree that the "extra reach" of the A700 over the A900 is not very significant, in fact it is only 7.9%, as shown on this web page:

http://www.robsphotography.co.nz/crop-factor-advantage-s700-s900.html

Tell us whether or not you agree with the following calculations:

I agree in principle; but your numbers are off by a little bit, because you're using a pixel size that's inferred from sensor size dimensions that are not precise, rather than using the actual pixel sizes published by the sensor manufacturers.

The 7.9% gain in reach (in favour of the A700) arises only because the pixel density of the A700 (in pixels per linear centimetre) is 7.9% greater than that of the A900 (1818 / 1685).

The actual gain is more like 8.2%. The A700 pixel size (as published by Sony) is 5.49 microns. The A900 pixel size (also as published by Sony) is 5.94 microns. So, rather than go to the trouble of (imprecisely) calculating some figures for pixels per centimeter, all you really had to do was ratio the sizes of the pixels themselves. And this ratio of 5.94/5.49 is equal to 1.082, or a gain of 8.2%.

Calculation of reach advantage: Reach of A700 with a 300mm lens = 458.3mm (300mm x 35.9/23.5).

The effective sensor width of the A900 is only approximately 35.9mm, just as the effective sensor width of the A700 is only approximately 23.5mm. That's the source of the small error in your calculations. Using the actual pixel size eliminates the need even to know the sensor size, or to calculate "effective" focal lengths (as you did below) when calculating the "reach advantage" being discussed. But if you did want to calculate the effective sensor size accurately, you would do it this way ...

For the A700:

Sensor width = 4272 pixels * .00549mm/pixel = 23.45328mm
Sensor height = 2848 pixels * .00549mm/pixel = 15.63552mm

For the A900:

Sensor width = 6048 pixels * .00594mm/pixel = 35.92512mm
Sensor height = 4032 pixels * .00594mm/pixel = 23.95008mm

For the Nikon D3S:

Sensor width = 4256 pixels * .00845mm/pixel = 35.9632mm
Sensor height = 2832 pixels * .00845mm/pixel = 23.9304mm

All a bit pedantic, I know -- but if you're going to be reporting an "advantage" or whatever, down to a tenth of a percent (as you are), you need to be calculating it the right way.

Reach of A900 when an image is cropped to the same image width as A700 = 424.7mm (6048 / 4272 x 300mm).

Gain in reach of the A700 = 7.9% (458.3mm / 424.7mm)

Regards,
--
Greg

Dave Oddie Veteran Member • Posts: 4,073
Re: How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Robsphoto wrote:

In these circumstances, would you agree that the "reach advantage" in favour of the A900 is about 42%, which is also equal to the 42% pixel density advantage (in linear terms)? This 42% reach calculation was explained in my opening post.

There is no reach advantage. If you crop the A900 image but end up with an identical photograph to the D3S shot, you would have to have been further away in the first place (for the A900 shot) given you were using lenses of the same focal length.

You have gained nothing because you have ended up with two identical photos of the same pixel dimensions.

If you crop an A900 image taken form the same spot with the same lens as your D3S photo to the same pixel dimensions you have ended up with a different photograph . You have cropped it.

The A900 gives you the ability to crop more aggressively compared to a D3S that is all. Talk of a reach advantage is misleading and unhelpful in my opinion.

Dave

 Dave Oddie's gear list:Dave Oddie's gear list
Sony SLT-A77 Sony DT 11-18mm F4.5-5.6 Sony DT 16-80mm F3.5-4.5 ZA Carl Zeiss Vario-Sonnar T* Sony 70-300mm F4.5-5.6 G SSM Sony 500mm F8 Reflex +4 more
Cyrus84 Senior Member • Posts: 1,862
Re: Cropping power of the Sony A900

Mike CH wrote:

Cyrus84 wrote:

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

Are you sure about that?

If you change from 400mm to 300mm and also change you position to maintain the same the scene, then perspective changes.

Exactly. That is what I am saying-- you cannot just crop to get the same field of view without changing the perspective.

But if you stay in the same place (rather, the optical center of the lenses stay in the same place), do the lens change and then crop to get the same scene, then perspective should stay the same.

See, I think it is similar to another poster above. You can't do that-- if you have 24 MP versus 12 MP, when you crop down to the same resolution, you aren't getting the same scene. Therefore, the higher MP camera has to back up to get the same FOV with the same resolution.

And doing so will completely change the perspective.
--
A700, Sigma 10-20, Tamron 28-75, Sigma 70-200, Minolta 50f1.7, Tamron 90 Macro

Cyrus84 Senior Member • Posts: 1,862
Re: How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Dave Oddie wrote:

Robsphoto wrote:

In these circumstances, would you agree that the "reach advantage" in favour of the A900 is about 42%, which is also equal to the 42% pixel density advantage (in linear terms)? This 42% reach calculation was explained in my opening post.

There is no reach advantage. If you crop the A900 image but end up with an identical photograph to the D3S shot, you would have to have been further away in the first place (for the A900 shot) given you were using lenses of the same focal length.

You have gained nothing because you have ended up with two identical photos of the same pixel dimensions.

I disagree with this. First, you did gain something-- you took the same picture but from a greater distance (however far you had to back up to take it). If you go forwards instead of backwards, that is like taking a picture of something 100 yards away when the other camera has to walk forward 25 yards to take the same picture. You gained that 25 yards of "something."

Secondly, as I said in another post, the perspective will completely change, so there is no way to have the same exact perspective when you use the same field of view and resolution. One of the three has to change-- either different perspective, or different field of view, or you can't crop to the same resolution.

If you crop an A900 image taken form the same spot with the same lens as your D3S photo to the same pixel dimensions you have ended up with a different photograph . You have cropped it.

The A900 gives you the ability to crop more aggressively compared to a D3S that is all. Talk of a reach advantage is misleading and unhelpful in my opinion.

Dave

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A700, Sigma 10-20, Tamron 28-75, Sigma 70-200, Minolta 50f1.7, Tamron 90 Macro

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